1. Field of the Invention
This invention relates to a vehicle headlamp arranged so as to switch beams between low and high beams by moving a shade.
2. Description of the Related Art
Vehicle headlamps are normally designed to send out low and high beams by making a reflector reflect light from a light source bulb forward. However, a difference in the light distribution pattern between the low and high beams required has made it customary to employ different light sources (discharge light emitting parts or filaments). However, vehicle headlamps using a single light source are also well known; in the case of a two-lamp type headlamp using a discharge bulb as a light source in particular, the single light source will have to be used very often.
In such a vehicle headlamp using a single light source, switching between low and high beams is conducted by the mechanical displacement of an optical element such as a light source, a reflector, a shade or the like. With respect to the vehicle headlamp shown in FIG. 8 in which beam switching is conducted by moving a shade, for example, a known arrangement is to longitudinally pivot a shade 2 around a longitudinal axis extending in the lateral direction.
In this vehicle headlamp, a light distribution pattern for the low beam is formed by shading part of light incident on the reflective surface 6a of a reflector 6 from a light source bulb 4 when the shade 2 is positioned as shown by a solid line in FIG. 8, whereas a light distribution pattern for the high beam is formed by reducing the shading quantity of light incident on the reflective surface 6a by the shade 2 when the shade 2 is pivoted forward and positioned as shown by a chain double-dashed line therein.
When the beam switching is conducted by mechanically driving the shade 2 as mentioned above, however, the shade 2 tends to produce a backlash in the low- or high-beam forming position because the clearance or backlash is inevitably produced in the mechanical coupling portion. If this sort of backlash occurs, the shade 2 will deflect (generate minute vibrations) because of vibrations during the travel of a vehicle and this may vary the area of the reflective surface 6a shielded by the shade 2. Therefore, the problem is that a light distribution pattern different from the intended light distribution pattern is formed in both cases of low and high beams.